Pilot fuel jet / slow jet

[speedcostsmoney]

Ok looking to change the fuel jet, stock is 37.5 up here in Canada, which has 0.0145 inch hole, the jet in the aluminium block under the float not the PAJ 1 UNDER AIRBOX, checked with dealer for avaiable sizes STOCK 37.5 , FOLLOWED BY 40.5 THEN COMES 45, Wondering if anyone has played with the slow jet

 

[Traumahawk]

In Seans kit, he usually sends out a 40....but most people dont need to go that large. Ive often wondered if changing out the size of the jet would the carbs LESS susceptible to getting trash in them, to where you have to do a shotgun and clean them out.

 

[Hooligans]

Why do you want to do this? I have been messing around with my carbs - trying to get a little more out of 3-7k rpm range but everything I've read says to leave those jets alone. What part of the power band will those jets change?

 

[Traumahawk]

Why do you want to do this? I have been messing around with my carbs - trying to get a little more out of 3-7k rpm range but everything I've read says to leave those jets alone. What part of the power band will those jets change?

The pilot fuel jets cover 0-4000 rpm at 1/8-1/4 throttle. Past 4000 you start getting into the needles....but it also depends on how much throttle your giving it as well. Past 7000, you should be getting into the mains.....but right where your talking about is usually controlled by the needles.

 

[tugla]

What's your set up for air filter and exhaust....or as mentioned what's up with the bike???

 

[sdt354]

I think #40 or larger for a pilot jet is something I'll do for a couple of reasons this off season. One, a lot of us turn the mixture screws out far enough to loose spring tension. Well, I do with my open boost set up to get a nice low end. The larger jet will allow the needles to be turned in closer to 2 1/2 turns. I think what Eric said about staying clean longer is the other reason I'll be doing this. The stock ones are small and crud up easy. #40 isn't a huge difference, but size matters. Yamaha new what they were doing but they tuned for emissions and all around riding. And, not with the after market exhaust many of us use, which changes things.
Steve-o

 

[speedcostsmoney]

the stock pilot fuel jets are set LEAN and the MAIN JET a little bigger than needed just to past the emission tests, now you know why your VMAX runs HOT ( STOCK VMAX ) THE pilot fuel jet is 0- 4000 rpm, but been reading on the ethernet and found out that this jet will affect top-end depending on a/f screws setting ,
shaved 0.025 off heads
dyna 3000
ufo 4 into 2 exhaust
stage 7
velocity stacks 3 inch
all 4 pods pull crankcase pressure
v-boost working of course
dyna coils
main jet dyno jet 185
3rd slot from square end
pilot fuel jet 37.5 / 0.0145 bored out to 0.018 runs good at 10 degres celcius
jsut looking for some feedback and maybe giving an option to my fellow VMAX RIDERS
THE MAX PULLS STRONG UP TO THE REV LIMITER 9500, NO DEAD SPOT JUST PURE ACCELERATION

 

[blaxmax]

the stock pilot fuel jets are set LEAN and the MAIN JET a little bigger than needed just to past the emission tests, now you know why your VMAX runs HOT ( STOCK VMAX ) THE pilot fuel jet is 0- 4000 rpm, but been reading on the ethernet and found out that this jet will affect top-end depending on a/f screws setting ,
shaved 0.025 off heads
dyna 3000
ufo 4 into 2 exhaust
stage 7
velocity stacks 3 inch
all 4 pods pull crankcase pressure
v-boost working of course
dyna coils
main jet dyno jet 185
3rd slot from square end
pilot fuel jet 37.5 / 0.0145 bored out to 0.018 runs good at 10 degres celcius
jsut looking for some feedback and maybe giving an option to my fellow VMAX RIDERS
THE MAX PULLS STRONG UP TO THE REV LIMITER 9500, NO DEAD SPOT JUST PURE ACCELERATION

How is your pilot jet and a/f mixture screws going to affect the top-end when they don't reach that range?

 

[davesax36]

I'm interested in the 40 pj thing. I know someone is running that. Not sure that's why idle always seems rich, though.

 

[one2dmax]

Most of the time if you need larger pilot jets you likely have the float settings wrong.

 

[davesax36]

Most of the time if you need larger pilot jets you likely have the float settings wrong.

I was thinking that the factory had probably tried some things.

 

[speedcostsmoney]

ok ok check it out FACTORY STOCK the YAMAHA VMAX comes LEAN JUST TO PASS EMMISION TESTS depending on country, carb settings will change, the REASON your VMAX runs hot is the PILOT FUEL JET, WHY because 0-4000 is the range that you will be riding 90% of the time, get caught in traffic WOW the temp needle goes up close to RED-LINE , THE ANSWER IS PILOT FUEL JET YOUR MAX IS RUNNING LEAN .......... THAT IS WHY I'M ASKING TI SEE IF ANYONE HAS PLAYED AROUND WITH THIS JET, BUT SEEMS MAYBE NOBODY HAS, FROM WHAT I HAVE READ, BIGGER PILOT FUEL JETS SMALLER MAIN JETS , BECAUSE THE PFJ WILL AFFECT THE TOP-END DEPENDING ON SIZE AND A/F SCREWS, BY THE WAY FOR THOSE WHO ASKED THE MAX RUNS GOOD , BUT WHY HAVE GOOD WHEN YOU CAN HAVE BETTER , NOT LOOKIN FOR GAS MILAGE OR ECONOMY, NOT LOOKIN TO SAVE THE WORLD, JUST LOOKIN FOR MAXIMUM MENTAL RIDE WHEN I GUN THE GAS, WITHOUT INVESTING THOUSANDS OF DOLLARS, BECAUSE IN THE END SPEED COSTS MONEY, 1000 DOLLARS FOR 10 HP IS EXPENSIVE, THATS ALL I GOTTA SAY ABOUT THAT

 

[Traumahawk]

I know that several people on here have thought about switching to the 40 PFJ....but havent. I'm one of them. Please post your experiences and let people know how its turned out.

And yes....the PFJ affects top end....that was the reason why I posted the pic that I did.

 

[davesax36]

Is that chart rpm independent? I can never remember. Like 4k is on the main fully, but up until then it's mixed more.

 

[Traumahawk]

Is that chart rpm independent? I can never remember. Like 4k is on the main fully, but up until then it's mixed more.

No....that chart is STRICTLY throttle dependent. So.....IF your 0-4000 rpm....AND using 1/8th of the throttle then your strictly on the PFJ. After that (still at the same 1/8 of the throttle) you start moving into where the needles will kick in, and they are active until about 7000ish rpm, then your fully into the mains.

BUT.....if your at 3000 rpm, and go full throttle, your kicking in the needles, and then going into the mains.

How Ive always set my needles....and its worked pretty well, at 2000-2500 rpm in 5th gear.....go to wide open throttle, if it bogs, you into the needle too much, and you need to move the clip closer to the blunt end. I might (and I say might) be leaving some hp on the table on the top end, but the drive-ability factor is thru the roof. 119 hp, with a heavy RC wheel, not too bad. I can also be on the intersate....5th gear, go full throttle, and maybe 1.5 seconds later the oil light comes on. The oil level is over halfway in the sight glass.

There are some companies that go for the ultimate in top end hp, but Ive heard from more than 1 person, you cant be piddling around town, and just go to wide open throttle.....you have to "roll" into it, or else it will bog.

Hope that helps....and I know more of an answer than you were looking for.

 

[blaxmax]

In EUR
150 mains
42.5 pilot
95 paj1
5EZ19-3 jet needle
pilot screw 2 1/2 turns out

 

[thor_eyerdhal]

No....that chart is STRICTLY throttle dependent. So.....IF your 0-4000 rpm....AND using 1/8th of the throttle then your strictly on the PFJ. After that (still at the same 1/8 of the throttle) you start moving into where the needles will kick in, and they are active until about 7000ish rpm, then your fully into the mains.

BUT.....if your at 3000 rpm, and go full throttle, your kicking in the needles, and then going into the mains.

How Ive always set my needles....and its worked pretty well, at 2000-2500 rpm in 5th gear.....go to wide open throttle, if it bogs, you into the needle too much, and you need to move the clip closer to the blunt end. I might (and I say might) be leaving some hp on the table on the top end, but the drive-ability factor is thru the roof. 119 hp, with a heavy RC wheel, not too bad. I can also be on the intersate....5th gear, go full throttle, and maybe 1.5 seconds later the oil light comes on. The oil level is over halfway in the sight glass.

There are some companies that go for the ultimate in top end hp, but Ive heard from more than 1 person, you cant be piddling around town, and just go to wide open throttle.....you have to "roll" into it, or else it will bog.

Hope that helps....and I know more of an answer than you were looking for.

Correct but with the Vmax carbs, needles are involved even at full throttle!
WOT, high RPM AFR is not the same with 150 main jets and S7 or stock needles.
With the big tip stock needle, you need a bigger main jet to achieve the same AFR.

 

[thor_eyerdhal]

In EUR
150 mains
42.5 pilot
95 paj1
5EZ19-3 jet needle
pilot screw 2 1/2 turns out

Yes
I tried the US setting
37.5 pilots and 90 air jet

Mysteriously, there is no way to make it works smoothy.
Idle is fine but all very light throttle cruises are crapy erratic.

Came back to EU settings and works fine.. :ummm:

 

[sdt354]

Even after soaking, ultra sonic cleaning,and reaming wire through it, I don't feel confident the slow jet is open to OEM size. I think I'm going the route of Speedcostmoney and using a pin vice to first clean it and have confidence that it is really flowing it's capacity, then maybe opening it up in very small increments. It's time consuming, but that's how I like to roll.
Steve

 

[Traumahawk]

Correct but with the Vmax carbs, needles are involved even at full throttle!
WOT, high RPM AFR is not the same with 150 main jets and S7 or stock needles.
With the big tip stock needle, you need a bigger main jet to achieve the same AFR.

True.....and thats why they say....tune from the top down. Thats also why I am running slightly different mains than the "recipe" calls for, because I'm still running the Factory Pro needles.

One other thing Dave that will really give you something to think about. Needles affect everything....including idle. When I went from the 3rd clip from the blunt end, to 1.5 clips from the blunt end, I had to go another 1/2 turn out on the a/f screws to get the idle back the way that it ways. That is something that isnt "supposed to happen" but it does.